Color: Multiple; Translucent to Opaque
Mohs Hardness: 5.5 – 6.5
Happy Opal Birthstone, October Babies!! The Romans gave opal its name, 'opalus', which means "precious stone.” And opals are precious stones indeed!
The characteristic that sets opal apart from any other gemstone is its exotic play-of-color, a phenomenon that causes light to break into rainbow colors in a variety of patterns when moved. Opal is made of tiny silica spheres that are arranged randomly like oranges in a basket and are compressed by the heavy desert land under which opals form. As light bounces off of these obscured curved surfaces, the spectral colors appear in a variety of patterns, flashing across the surface.
One pattern you will not see in a naturally formed opal is “snake-skin”, which is the #1 identifier of synthetic (aka: man-made) opal. When people make opal in a laboratory, they don’t seem to be able to get the spheres to fall randomly in that so called “orange basket”, as they do in nature. Instead, laboratory opal arranges the silica spheres in perfect rows that are then compressed, creating this even, predictable pattern of play-of-color.
Because snake-skin is so easily identifiable, opal cutters have gotten creative, sometimes placing the axis of the snake-skin so it is not face-up, causing the play-of-color to look more like a brush-stroke. Don’t be fooled! Tilt and rock your opal if you think the play-of-color is too consistent and see if the snake-skin appears (note: you may need magnification to see it)!
There are several varieties of opal, each named according to the base color of the gem. The most familiar opal we see on the market in the United States is the White Opal, which has a white or light body color with play-of-color.
Contrary to its name, the body color of black opal can be dark green, dark blue or gray, as well as black. Black opal with red play-of-color is considered the most valuable type of opal.
Boulder Opal is an opal variety in which a thin seam of opal is cut to include its ironstone matrix in order to add strength and a dark background color.
Unlike other varieties of opal, Fire opal comes in an intensely saturated palette of base colors from yellow to fiery red. The base color is considered to be fire opal's most important value factor. Fire opal may or may not display play-of-color, but when it does WOW. It’s beautiful. Faceted transparent fire opals that display play-of-color are extraordinarily rare and command premium prices. [See Below For Fire Opal!]
It is important to note that while play-of-color is opals most remarkable characteristic, not all opals display play-of-color. Pink opal, for example, does not display the play-of-color phenomenon. Opals that do not display play-of-color are referred to as “Potch” opals… I guess it’s because they really “potched” up that whole opal thing, don’t you think?
Opal Fun Fact!: Although they are formed in desert climates, opals are the camels of gemstones and contain between 3-20% water! It is not recommended to keep opals in safety deposit boxes or other air-tight storage areas, as they can dehydrate and crack, which is called “Crazing”. I think we all craze a little when thirsty… [Insert MIRAGE JOKE here... I mean, come on! ;-) Opal is a thirsty desert stone!]
This beautiful Fire Opal is displaying a large amount of crazing throughout. Bummer.
Recently, I have been on a particularly large opal kick. Check out some of my recent opal cufflink creations: